By immunizing nonhuman primates and rabbits with various normal and leukemia cell preparations we have been able to define by cytotoxicity testing certain antigens which were present on normal and/or leukemia cells which have been helpful in the diagnosis and nosology of human leukemias. These antisera are now being studied by radioimmunoprecipitation and gel electrophoresis with leukemia cell membrane antigens and primate C type virus antigens which have been radiolabeled by various techniques.